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Date: Wed, 23 Jan 2019 12:55:35 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Michal Hocko <mhocko@...nel.org> Cc: linux-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, Gary R Hook <ghook@....com>, Heiko Carstens <heiko.carstens@...ibm.com> Subject: Re: [PATCH 2/2] debugfs: return error values, not NULL On Wed, Jan 23, 2019 at 12:06:28PM +0100, Michal Hocko wrote: > On Wed 23-01-19 11:28:14, Greg KH wrote: > > When an error happens, debugfs should return an error pointer value, not > > NULL. This will prevent the totally theoretical error where a debugfs > > call fails due to lack of memory, returning NULL, and that dentry value > > is then passed to another debugfs call, which would end up succeeding, > > creating a file at the root of the debugfs tree, but would then be > > impossible to remove (because you can not remove the directory NULL). > > > > So, to make everyone happy, always return errors, this makes the users > > of debugfs much simpler (they do not have to ever check the return > > value), and everyone can rest easy. > > How come this is safe at all? Say you are creating a directory by > debugfs_create_dir and then feed the return value to debugfs_create_files > as a parent. In case of error you are giving it an invalid pointer and > likely blow up unless I miss something. debugfs_create_files checks for invalid parents and will just refuse to create the file. It's always done that. > I do agree that reporting errors is better than a simple catch all NULL > but this should have been done when introduced rather than now when most > callers simply check for NULL as a failure. I'm fixing up all the "NULL is a failure" callsites in the kernel, see lkml for the first round of those patches. thanks, greg k-h
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